Hall-Heroult Process. • Electrochemical Process to Reduce Alumina to Aluminum . – Alumina is dissolved in a molten fluoride solvent called cryolite. 2 Al. 2. O. Aluminium is produced according with the Hall-Heroult process. During this complex electrolyte two-phase electrolysis, it is difficult to model the current. Hall-Héroult process: metallurgy: Electrolytic smelting: In the Hall-Héroult smelting process, a nearly pure aluminum oxide compound called alumina is dissolved.
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Aluminum, an overview Aluminum properties Aluminum discovery and extraction – A brief history Process basics Prebake and Soderberg Detailed description of a cell and its basic functioning How an aluminum smelter is made Process thermodynamic hsroult Enthalpy Process thermodynamic – Free Energy Cell voltage The voltage drop in the electrolyte Theoretical yall of aluminum Some important figures Bath chemistry Electrolyte properties Current efficiency The cryolite ledge Cell thermal balance Anode effect Influence of hdroult fields Inert anode technology Useful links More The density rpocess the electrolyte should be less than 2.
Elemental aluminium cannot be produced by the electrolysis of an aqueous aluminium salt because hydronium ions readily oxidize elemental aluminium. Bars of aluminium were exhibited alongside the French crown jewels at the Exposition Universelle ofand Emperor Napoleon III of France was said to have reserved his few sets of aluminium dinner plates and eating utensils for his most honored guests.
Alumina is added to the electrolyte from between the anodes in prebake technology using cells. The aluminum is produced extracting it from the aluminum oxide Al 2 O 3called also alumina, through an electrolysis process driven by electrical current.
More material to the top of the anode is continuously added in the form of briquettes made from coke and pitch. Particulates are captured using electrostatic or bag filters. The liquid aluminium is removed from the cell via a siphon every 1 to 3 days in order to avoid having to use extremely high temperature valves and pumps.
In modern facilities fluorides are almost completely recycled to the cells and therefore used again in the electrolysis.
Hall–Héroult process – Wikipedia
The electrolytic mixture is sprinkled with coke to prevent the anode’s oxidation by the oxygen evolved. Escaped HF can be neutralized to its sodium salt, sodium fluoride. Retrieved from ” https: Oxidation of the proceess anode increases the electrical efficiency at a cost of consuming the carbon electrodes and producing carbon dioxide.
Temperature within the cell is maintained via electrical resistance. The process uses as electrolyte a molten salts called Cryolite Na 3 AlF 6 capable of dissolve the alumina.
The Hall-Héroult Process Basics – The Aluminum Smelting Process
As a result, the heroulf bond between aluminum and oxygen in the alumina is broken, the aluminum is deposited in the bottom of the cell, where a molten aluminum deposit is found, while the oxygen reacts with the carbon of the anodes producing carbon dioxide CO 2 bubbles.
Recycled aluminum requires no electrolysis, thus it does not end up in this process. This page was last edited on 13 Decemberat In other projects Wikimedia Commons. The alumina reduction process is described by the following reaction:.
Carbon anodes are immersed into the electrolyte usually referred as the “bath” carrying electrical current which then flows into the molten cryolite containing dissolved alumina. Collected aluminium from different cells in a procwss is finally melted together to ensure uniform product and made into e. Cathodes are typically replaced every 2—6 geroult.
Aluminium fluoride AlF 3 is usually added to the electrolyte. The exhaust is primarily CO 2 produced from the anode consumption and hydrogen fluoride HF from the cryolite and flux AlF 3.
This increases the resistance of the cell when smaller areas of the electrolyte touch the anode. Chemical processes Aluminium industry Electrolysis. In addition to AlF 3other additives like lithium fluoride may be added to heroulh different properties melting point, density, conductivity etc. Besides having a relatively low melting point, cryolite is used as an electrolyte because among other things it also dissolves alumina well, conducts electricity, dissociates electrolytically at higher voltage than alumina and has a lighter density than aluminum at the temperatures required by the electrolysis.
The inside of the cell’s bath is lined with cathode made from procezs and pitch. Prebake technology is named after its anodes, which are baked in very large gas-fired ovens at high temperature before being lowered by various heavy industrial lifting systems into the electrolytic solution.
It occurs in many minerals but its primary commercial source is bauxitea mixture of hydrated aluminium oxides and compounds of other elements such as iron. This heats up the gas layer and causes it to expand thus further reducing the surface area where electrolyte and anode are in contact with each other.
The following is a schematic picture of an aluminum electrolysis cell: The aluminium sinks to the bottom of the electrolytic cell, where it is periodically collected. Once passed through the bath, the electrical current flows into the molten aluminum deposit and is then collected by the bottom of the pot, usually called “cathode”.
There usually are 24 prebaked anodes in two pocess in one cell. The lost heat from the smelting operation is used to bake the briquettes into the carbon form required for reaction with alumina.
In reality much more CO 2 is formed at the anode than CO:. It also induces the formation of tetrafluoromethane CF 4 in significant quantities, increased formation of CO and to lesser extent also causes the formation of hexafluoroethane C 2 F 6. Pitch resin or tar is used as a binder.
pprocess Views Read Edit View history. Electrochemistry Gas cracker Standard electrode potential data page Electrology. Cathodes also degrade during electrolysis, but much more slowly than anodes do, and thus they need neither be as high in purity nor be maintained as often. This requires the whole cell to be shut down.
Retrieved 19 April Anode effect decreases the energy-efficiency and the aluminium production of the cell.